Eighty-seven newborns at Scarborough General Hospital are being tested after they may have been exposed to tuberculosis by an infected nurse.
Dr Peter Azzopardi, chief of pediatrics at the hospital, said the potential exposure happened to babies in the neonatal unit.
He says babies in the neonatal unit who may have been exposed are now being tested as a precaution.
"There is a minimal or miniscule risk of the babies catching tuberculosis," Azzopardi said. "The problems with babies and tuberculosis is that their illness could be not very specific and it could rapidly escalate."
So far none of the babies have tested positive.
It's unclear how the nurse caught tuberculosis. The hospital says she reported her symptoms as soon as she felt ill, and is now at home recovering.
Toronto had about 300 cases of the airborne disease in 2011, mostly affecting people who had been in countries where the condition is problematic.
Most patients in the city make a full recovery with proper treatment, but worldwide nearly 5,000 people die every day from the bacteria.
The disease spreads through coughs and sneezes and can cause fever, persistent cough, fatigue, weight loss, night sweats and chest pain.
Experts say people in Canada can become sick and not have the impression that their illness is something as serious as tuberculosis.